Hybrid fiber combines strength of metal core and elasticity of rubber shell

Abstract

Tough, biological materials (e.g., collagen or titin) protect tissues from irreversible damage caused by external loads. Mimicking these protective properties is important in packaging and in emerging applications such as durable electronic skins and soft robotics. This paper reports the formation of tough, metamaterial-like core-shell fibers that maintain stress at the fracture strength of a metal throughout the strain of an elastomer. The shell experiences localized strain enhancements that cause the higher modulus core to fracture repeatedly, increasing the energy dissipated during extension. Normally, fractures are catastrophic. However, in this architecture, the fractures are localized to the core. In addition to dissipating energy, the metallic core provides electrical conductivity and enables repair of the fractured core for repeated use. The fibers are 2.5 times tougher than titin and hold more than 15,000 times their own weight for a period 100 times longer than a hollow elastomeric fiber.




Full text: http://advances.sciencemag.org/content/5/2/eaat4600






Figure 1B compares the force versus strain responses of a solid gallium rod, an empty SEBS fiber, and a Ga-SEBS metamaterial fiber (see fig. S2 for stress-strain data). In Fig. 1B, each sudden decrease in force corresponds to a break in the metallic core of the Ga-SEBS fiber, after which a polymer bridge forms from the encasing polymer. After each break, the force needed to maintain a constant rate of extension increases steadily as the bridge is strained, until eventually the metallic core fractures again and the cycle repeats itself. During these cycles, the strain localizes primarily in the polymer bridges between the breaks, which keeps the overall stress high regardless of the macroscopic strain. This behavior generates a sawtooth-shaped curve centered about the force needed to break the metallic core (see note S1 for additional details) and provides an effective and continuous energy dissipation method. The fiber sustains approximately the same force as the force needed to break the metallic core, but for almost six times the amount of strain.